Conventionally in the field of mechanical engineering, parts subjected to forces of tension and/or of compression can include an elastically deformable element associated with a load cell, in such a way as to measure an elastic deformation in order to evaluate these forces. In order to obtain an accurate measurement, the amplitude of the elastic deformation must be relatively large under the forces commonly sustained in normal operating mode.
However, a connecting rod of an aeronautical mechanism is dimensioned to support critical forces, in a failing operating mode, that are much higher than the forces that are applied in normal operation. However, such critical forces risk generating a plastic deformation of the elastically deformable element, which renders it useless and requires it to be replaced in order to again be able to take measurements of forces.
EP-A-2 067 697 describes such a connecting rod for aeronautical construction, including at least one shaft intended to transmit forces applied essentially in tension and/or in compression when the connecting rod is in service. An elastically deformable element is integral with the shaft in order to react to these forces, and configured to be deformed elastically under the effect of these forces. One or several load cells are associated with the deformable element in such a way as to measure the elastic deformation in order to evaluate the forces. Moreover, the connecting rod has a safety member integral with the deformable element and at a distance from the shaft when the connecting rod is at rest. This safety member is provided in order to limit the movements of the shaft when the elastic deformation exceeds a determined limit, in such a way as to transmit the excess portion of the forces. Such a safety member therefore makes it possible to protect the elastically deformable element, by “short circuiting” it when the forces exceed its elastic limit. The element protected as such can have an elastic deformation of large amplitude during normal operation, in such a way as to take accurate measurements of forces.
However, such a connecting rod is not entirely satisfactory. Indeed, in order to take accurate measurements, the connecting rod must include a substantial number of strain gauges, more preferably at least four gauges. Because of this, the electronic post-processing chain associated with these gauges is complex. Moreover, these gauges are generally glued onto the deformable element. However, the glue does not resist well to ageing in the operating conditions of the connecting rod and of the deformable element. As such, the use of this glue creates a substantial sealing constraint and reduces the reliability of the measurements over time.
US-A-2005 178 215 describes another connecting rod for aeronautical construction. This connecting rod includes a spring which is connected to a shaft and configured, on the one hand, to react to the forces applied to the shaft and, on the other hand, to have an elastic deformation under the effect of these forces. The connecting rod further comprises a sensor associated with the spring and configured in order to determine the forces. The sensor is housed at its two ends in the spring. The use of such a spring is not entirely satisfactory, in particular in terms of measurement accuracy.
The purpose of this invention is to propose a connecting rod that makes it possible to take measurements of forces simply, accurately and reliably, during its entire life cycle.
For this purpose, the invention relates to a connecting rod for an aeronautical actuator system, having at least one shaft configured to transmit forces applied essentially in tension and/or in compression along a longitudinal axis of the connecting rod when the connecting rod is in service, an elastically deformable element which is connected to the shaft and configured, on the one hand, to react to the forces applied to the shaft and, on the other hand, to have an elastic deformation under the effect of these forces, with the deformable element including a peripheral part which is rigidly connected to a member of the connecting rod where the shaft is slidably mounted, and measurement means associated with the deformable element and configured to determine the forces, with the measurement means being at least partially housed in the deformable element.
According to the invention the deformable element has a central part which is elongate along the longitudinal axis of the connecting rod, which is rigidly connected to the shaft and in which the measurement means are at least partially housed, and an intermediate part which runs transversally to the central part and which connects the central part and the peripheral part.
As such, the invention makes it possible to improve the accuracy and the reliability of the measurement system. In particular, the measurement means are measurement means for displacement, configured to determine the forces using the displacement of the deformable element. This deformable element has the form of a diaphragm, of which the structure and the deformations are well controlled. Due to the relative arrangement of the measurement means and of the deformable element, these measurements can be taken in a reactive manner during the deformations of this element. Moreover, the risk of the measurement means separating from the deformable element is reduced. In other words, the measurement system has improved resistance to ageing. Also, this measurement system operates in a simple manner, without requiring a complex electronic post-processing chain.
According to other advantageous characteristics of the invention, taken separately or in combination, an example is: the central part, the peripheral part and the intermediate part of the deformable element are integrally formed; the measurement means include at least one linear displacement sensor, this sensor being at least partially housed in the deformable element; the measurement means include at least two linear displacement sensors positioned parallel to one another on either side of the longitudinal axis of the connecting rod, each sensor being at least partially housed in the deformable element; or each sensor is rigidly fixed to the deformable element and mobile in a complementary element configured to transform a displacement measurement of the sensor into a value of forces applied to the deformable element; the measurement means are closer to the longitudinal axis of the connecting rod than to the periphery of the connecting rod; the shaft is arranged slidingly in the member which is rigidly connected to the peripheral part of the deformable element, such that a displacement of the shaft under the effect of the forces results in a displacement of the central part of the deformable element; the shaft includes means of abutment which are, on the one hand, at a distance from the member and from the deformable element when the connecting rod is at rest and, on the other hand, configured to limit the forces applied in traction and/or in compression on the deformable element when the elastic deformation exceeds a determined limit, in such a way as to transmit the excess portion of the forces; the deformable element is made of high-strength stainless steel or of titanium; the connecting rod comprises a central case and two units arranged symmetrically in relation to the case along its longitudinal axis, with each unit comprising a deformable element, a shaft and measurement means.
The invention also has for purpose an aeronautical mechanism including at least one connecting rod such as mentioned hereinabove. The connecting rod is interposed between a rotary actuator and a flap panel so as to transfer force from the rotary actuator and the flap panel. The aeronautical mechanism is configured to move the flap panel and hold it in extreme or intermediate positions.